I did my first update in a week or so today, and now find that Gnome is
doing very strange things indeed.

Firstly, gnome-panel appears to be gone.

Can anyone confirm that this is affecting them too or if I'm just going
nuts?

It seems that GNOME 2.10 is moving into unstable from experimental. I
don't know if the transition is working fine on AMD64, but so far I
haven't experienced the same problems as you and I've updated all the
components I could (almost all libraries) without having any noticeable
failure so far.
Greetings,

Thanks Javier, don't upgrade any more yet until it's finished as in
Jim's post.